Recently, a wiring is formed on a substrate such as a semiconductor wafer or a liquid crystal substrate to form a circuit on a surface of the substrate. The wiring is typically made of, instead of aluminum, copper having low electric resistance and high reliability. Since, however, copper tends to be easily oxidized as compared to aluminum, it is required to plate a surface of the copper wiring with a metal having high electromigration resistance in order to prevent the surface of the copper wiring from being oxidized.
A plating process is performed by supplying an electroless plating liquid onto the surface of the substrate on which the copper wiring is formed. For example, the substrate is held on a substrate holding/rotating device, and by supplying the electroless plating liquid while rotating the substrate holding/rotating device, a uniform flow of the plating liquid is formed on the surface of the substrate. As a result, a plating process is performed on the entire surface of the substrate uniformly (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Laid-open Publication No. 2001-073157